Drilling and blasting operations are used for controlled rock removal in mining, road construction, tunnelling, and rock sculpturing. Strategically spaced holes are drilled into the rock, powder charges are placed in the holes, the holes are sealed by back-filling with loose rock or other "stemming" material, and the charges are detonated. Diagram FIG. 1 shows the cross section of a typical prepared basic blast hole configuration.
For some blasting situations it is desireable to use air decking, a technique which provides an air space between the powder charge and the stemming material, as typically shown in FIG. 2. The air space allows blasting forces to be exerted over a greater length of the drill hole while using a reduced powder charge. A plug is used to suspend the stemming material above the powder charge, thereby creating the air space. An ideal plug completely seals the hole to prevent gasses from pushing upwards or "rifling" out of the blast hole. This results in maximum force application to the rock surface within the blast chamber.
In some cases, desirable effects are obtained by using multiple powder charges in the same blast hole, separating the charges with multiple plugs as typically shown in FIG. 3. In others, it is desireable to blast the hole in sections starting at the top and working downward. For these situations, the hole must be plugged a certain distance from the top to allow for the upper section of rock to be blown away first. A positive seal is needed for these operations to ensure that the force of the blast does not push downward into the bottom of the hole. Sand is filled in on top of the plug and stemming material is back-filled on top of the powder to help divert the force of the blast outward, into the rock, as typically shown in FIG. 4.
Escaping gasses, blown upwards around blocking mechanisms and through stemming material during detonation, may reduce the effectiveness of blasting. The most effective air decking blocking mechanisms, or plugs, are therefore those which provide positive gas sealing capabilities.
Therefore, there is a need for a safe, easy to use, inexpensive way to provide an air-tight borehole seal for use in blasting applications.